1*2175Sjp161948=pod
2*2175Sjp161948
3*2175Sjp161948=head1 NAME
4*2175Sjp161948
5*2175Sjp161948DH_generate_parameters, DH_check - generate and check Diffie-Hellman parameters
6*2175Sjp161948
7*2175Sjp161948=head1 SYNOPSIS
8*2175Sjp161948
9*2175Sjp161948 #include <openssl/dh.h>
10*2175Sjp161948
11*2175Sjp161948 DH *DH_generate_parameters(int prime_len, int generator,
12*2175Sjp161948     void (*callback)(int, int, void *), void *cb_arg);
13*2175Sjp161948
14*2175Sjp161948 int DH_check(DH *dh, int *codes);
15*2175Sjp161948
16*2175Sjp161948=head1 DESCRIPTION
17*2175Sjp161948
18*2175Sjp161948DH_generate_parameters() generates Diffie-Hellman parameters that can
19*2175Sjp161948be shared among a group of users, and returns them in a newly
20*2175Sjp161948allocated B<DH> structure. The pseudo-random number generator must be
21*2175Sjp161948seeded prior to calling DH_generate_parameters().
22*2175Sjp161948
23*2175Sjp161948B<prime_len> is the length in bits of the safe prime to be generated.
24*2175Sjp161948B<generator> is a small number E<gt> 1, typically 2 or 5.
25*2175Sjp161948
26*2175Sjp161948A callback function may be used to provide feedback about the progress
27*2175Sjp161948of the key generation. If B<callback> is not B<NULL>, it will be
28*2175Sjp161948called as described in L<BN_generate_prime(3)|BN_generate_prime(3)> while a random prime
29*2175Sjp161948number is generated, and when a prime has been found, B<callback(3,
30*2175Sjp1619480, cb_arg)> is called.
31*2175Sjp161948
32*2175Sjp161948DH_check() validates Diffie-Hellman parameters. It checks that B<p> is
33*2175Sjp161948a safe prime, and that B<g> is a suitable generator. In the case of an
34*2175Sjp161948error, the bit flags DH_CHECK_P_NOT_SAFE_PRIME or
35*2175Sjp161948DH_NOT_SUITABLE_GENERATOR are set in B<*codes>.
36*2175Sjp161948DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be
37*2175Sjp161948checked, i.e. it does not equal 2 or 5.
38*2175Sjp161948
39*2175Sjp161948=head1 RETURN VALUES
40*2175Sjp161948
41*2175Sjp161948DH_generate_parameters() returns a pointer to the DH structure, or
42*2175Sjp161948NULL if the parameter generation fails. The error codes can be
43*2175Sjp161948obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
44*2175Sjp161948
45*2175Sjp161948DH_check() returns 1 if the check could be performed, 0 otherwise.
46*2175Sjp161948
47*2175Sjp161948=head1 NOTES
48*2175Sjp161948
49*2175Sjp161948DH_generate_parameters() may run for several hours before finding a
50*2175Sjp161948suitable prime.
51*2175Sjp161948
52*2175Sjp161948The parameters generated by DH_generate_parameters() are not to be
53*2175Sjp161948used in signature schemes.
54*2175Sjp161948
55*2175Sjp161948=head1 BUGS
56*2175Sjp161948
57*2175Sjp161948If B<generator> is not 2 or 5, B<dh-E<gt>g>=B<generator> is not
58*2175Sjp161948a usable generator.
59*2175Sjp161948
60*2175Sjp161948=head1 SEE ALSO
61*2175Sjp161948
62*2175Sjp161948L<dh(3)|dh(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
63*2175Sjp161948L<DH_free(3)|DH_free(3)>
64*2175Sjp161948
65*2175Sjp161948=head1 HISTORY
66*2175Sjp161948
67*2175Sjp161948DH_check() is available in all versions of SSLeay and OpenSSL.
68*2175Sjp161948The B<cb_arg> argument to DH_generate_parameters() was added in SSLeay 0.9.0.
69*2175Sjp161948
70*2175Sjp161948In versions before OpenSSL 0.9.5, DH_CHECK_P_NOT_STRONG_PRIME is used
71*2175Sjp161948instead of DH_CHECK_P_NOT_SAFE_PRIME.
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73*2175Sjp161948=cut
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